"A drowning man will catch at a straw." 
  
 
THE LAST STRAW (English) 
  
That which constitutes the final limit of endurance. 
 
     
THE STRAW THAT BROKE THE CAMEL'S BACK (English)

The last in a series of cumulative irritations, unpleasant tasks, reponsibilities, or remarks (especially a seemingly minor one) that pushes a person's patience and endurance beyond his or her limits; a final setback, one which demoralizes someone or destroys an enterprise or other matter.
 
The camel, a beast of burden, stubbornly refuses to move if given too heavy a load to bear. Although a single straw on a camel's back has an insignificant weight, many straws can produce a burder which may be too heavy to bear, figuratively breaking the camel's back.
 
By implication, then, a person subjected to one too many misfortunes or vexations may be pushed beyond his or limits and respond suddenly and explosively in a manner that seems disproportionate to the provocation. This expression has several variations, the most common of which is the last straw (see above).
 
 
NO SE DUERME EN LAS PAJAS (Spanish) 
  
The Spanish translation, "He doesn't fall asleep in the straw" is equivalent to the English, "He doesn't let the grass grow under his feet." 
  
Even though straw is good to sleep on, the word usually means "worthless." Thus, in Spanish, "to quarrel over straws" is to quarrel over trifles. The English, on the other hand, say, "I don't give a straw."